This invention relates to a dynamoelectric machine and particularly to an electric motor adapted to be mounted within a separate enclosure.
In various electrical applications, a rotary dynamoelectric machine, such as a rotary motor, is used as a drive mechanism. In certain applications, a motor is mounted within a separate housing such as a fan housing with the motor shaft coupled to drive a fan blade. The motor includes an outer annular stator unit of any known or suitable construction. A rotor unit is rotatably mounted within the stator. A standard conventional motor will include an annular stator core of the stator unit fixedly mounted in any suitable manner within an heavy outer tubular motor frame. The frame projects axially from the ends of the stator core beyond the ends of the stator winding. The ends of the frame are machined and corresponding machined end plates are interconnected to the ends of the motor frame as by through bolts or other securement devices. Rotor bearings are secured one each within each of the end plates in appropriate alignment. The rotor shaft is journaled in the bearings with the rotor core aligned with the stator core. The frame and end frames enclose the electrical winding as well as providing necessary structural strength to support the rotor unit within the stator unit. The machined frame ends and end plates accurately locate the bearings to support the rotor core and the stator core with an air gap therebetween to permit free rotation of the rotor core. In rotating electric motor, the air gap between the rotor core and the stator core must be maintained within specified clearance limits. In many applications, efficient motor design requires minimizing of the air gap between the stator and the rotor.
Strong magnetic forces are created between the cores of the stator unit and the rotor unit, and a substantial frame is necessary to hold and maintain the necessary air gap between the rotor core and stator core. In addition, radial side loads may be applied to the shaft by the driven load creating even larger forces on the rotor support structure. The magnetic forces plus the radial side load forces can result in bearing radial loads of several hundred pounds which requires rigid bearing supports, and a corresponding supporting frame, to firmly support the rotor within the stator without danger of the rotor bridging the air gap and damaging the members.
In many applications, the motor frame is not necessary because the motor is housed within a separate housing. The standard motor with the motor frame can be used. In those applications however, a frameless motor can be used wherein the stator unit can be mounted directly to the frame or a mounting base of the driven element. The rotor unit is then appropriately supported by appropriate bearing structures interconnected to each other and/or to the driven element support structure.
Although frameless motors have been suggested in the prior art, relatively complex and costly bearing support structures for the rotor and the supporting bearing assembly is provided. Further, each application generally requires a custom bearing support structure.
The prior art patents thus disclose various motor structures including separate stator units and enclosed rotor units. For example, U.S. Pat. No. 4,244,099 which issued Jan. 13, 1981 discloses an electric motor adapted to be mounted as a part of a gear train housing. The motor consists of an outer annular stator unit within an outer main frame and a separate enclosed rotor unit which extends through the stator and extends therefrom for mounting of the rotor with a press fit within an opening in the gear frame. The rotor is supported by the opening in the base wall of the housing while the stator unit is supported and located within an enlarged recess in the housing. U. S. Pat. Nos. 4,598,218 and 4,510,679 disclose similar high speed rotors where the rotor core and winding is protected by an encircling protective shell which closely fits and is secured about the core. Special shaft units project outwardly from the opposite ends of the core for mounting in separate bearing assemblies mounted in separate supports of the outer enclosure structure.
There is a need for a relatively simple but reliable and effective frameless motor construction having an integrated support for the rotor which will establish and maintain the designed running air gap over the useful life of the dynamoelectric machine.